Mechanical and chemical-mechanical planarization processes (collectively “CMP”) remove material from the surface of micro-device workpieces in the production of microelectronic devices and other products. FIG. 1 schematically illustrates a rotary CMP machine 10 with a platen 20, a carrier assembly 30, and a planarizing pad 40. The CMP machine 10 may also have an under-pad 25 between an upper surface 22 of the platen 20 and a lower surface of the planarizing pad 40. A drive assembly 26 rotates the platen 20 (indicated by arrow F) and/or reciprocates the platen 20 back and forth (indicated by arrow G). Since the planarizing pad 40 is attached to the under-pad 25, the planarizing pad 40 moves with the platen 20 during planarization.
The carrier assembly 30 has a chuck or head 31 with a chamber 32, a retaining member 33 around a perimeter of the head 31, and a backing assembly in the chamber 32. The backing assembly includes a plate 34 and a diaphragm 35 on the exterior of the plate 34. The plate 34 can have a plurality of holes through which air can pass to act against the diaphragm. The carrier assembly 30 also has a pneumatic line 36 through a shaft 37, a rotary coupling 38 on the shaft 37, and an actuator assembly 39 (shown schematically) that rotates the shaft 37. The actuator assembly 39 translates or rotates the head 31 (arrows I and J respectively), and the rotary coupling 38 couples a pneumatic pump to the pneumatic line 36. In operation, a positive air pressure is applied to the plate 34 by pumping air into the chamber 32 via the pneumatic line 36, or a vacuum is applied by drawing air from the chamber 32 via the pneumatic line 36.
The planarizing pad 40 and a planarizing solution 44 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of a micro-device workpiece 12 in the head 31. The planarizing solution 44 may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the surface of the micro-device workpiece 12, or the planarizing solution 44 may be a “clean” non-abrasive planarizing solution without abrasive particles. In most CMP applications, abrasive slurries with abrasive particles are used on non-abrasive polishing pads, and clean non-abrasive solutions without abrasive particles are used on fixed-abrasive polishing pads.
To planarize the micro-device workpiece 12 with the CMP machine 10, the carrier assembly 30 presses the workpiece 12 face-downward against the planarizing pad 40. More specifically, the carrier assembly 30 generally presses the micro-device workpiece 12 against the planarizing solution 44 on a planarizing surface 42 of the planarizing pad 40, and the platen 20 and/or the carrier assembly 30 moves to rub the workpiece 12 against the planarizing surface 42. As the micro-device workpiece 12 rubs against the planarizing surface 42, the planarizing medium removes material from the face of the workpiece 12.
The CMP process must consistently and accurately produce a uniformly planar surface on the workpiece 12 to enable precise fabrication of circuits and photo-patterns. A non-uniform surface can result, for example, when material is removed more quickly in one area than another during CMP processing. To compensate for the non-uniform removal of material, the carrier head shown in FIG. 1 can adjust the downforce by controlling the air pressure in the chamber 32. These carrier heads, however, have several drawbacks. For example, the diaphragm may rip during a planarizing cycle. When this occurs, the planarizing machine is programmed to apply a vacuum in the chamber 32 for holding the workpiece in the head 31. This causes the planarizing solution 44 to back-flow into the chamber 32 and up through the pneumatic line 36 to the rotary coupling 38. The planarizing solution fouls the rotary coupling 38, the pneumatic line 36, and the plate 34. The rotary coupling 38 may fail because of such fouling, which can cause unnecessary downtime for repairing the head 31. The fouling of the pneumatic line 36 and plate 34 may also make it difficult to control the distribution of backside pressure on the workpiece because the planarizing solution can obstruct the pneumatic line 36 or the holes in the plate 34. This often results in non-uniform surfaces on workpieces.